1. Field of the Invention
The present invention relates to a magnetoresistance film and a method of manufacturing such a magnetoresistance film, and more particularly to a magnetoresistance device and a magnetoresistance magnetic head which incorporate such a magnetoresistance film. More specifically, the present invention is concerned with a highly sensitive magnetoresistance film having an artificial superlattice film structure exhibiting a large magnetic reluctance and suitable for use in magnetoresistance device such as a magnetic sensor or the like or a magnetoresistance magnetic head such as a playback head for a magnetic disc drive, and a method of manufacturing such a highly-sensitive magnetoresistance film.
2. Description of the Relevant Art
Magnetoresistance films are widely used as a magnetoresistance device for detecting a magnetic field in the fields of magnetic sensors, magnetic heads, rotation detectors, position detectors, etc.
For example, Permalloy, which is a typical material for magnetoresistance films, is used in the magnetic sensor of a magnetoresistance head (MR head) for reading a weak signal magnetic field in the art of magnetic recording because its anisotropic magnetic field has a small level of about 4 gausses and it has very good soft magnetic characteristics.
However, the rate of change of the magnetoresistance of Permalloy is of about several percent at maximum, and hence Permalloy does not provide sufficient sensitivity for high-density magnetic recording trends that appear to develop further in the future.
The magnetoresistance of Permalloy is greatly governed by the direction of a bias magnetic field applied thereto. If Permalloy is used in the magnetic sensor of an MR head, then it is necessary to control the direction of the anisotropy of the material.
Much attention has been directed in recent years to artificial superlattices which are composed of alternating layers of different metals each several atoms thick. There has been reported artificial superlattice composed of a laminated structure of magnetic layers (Fe layers) and conductive layers (Cr layers) and exhibiting a large magnetoresistance of about several tens percent (see Physical Review Letters, Vol. 61, page 2472, 1988). The reported artificial superlattice is expected to find an application in magnetoresistance devices.
A subsequent effort has resulted in an artificial superlattice composed of a laminated structure of magnetic layers (Co layers) and conductive layers (Cu layers) and also exhibiting a large magnetoresistance (see Physical Review Letters, Vol. 66, page 2152, 1991).
The inventors have, however, found that attempts to use an artificial superlattice film as a magnetoresistance device in practical applications have encountered certain problems with regard to maintaining a large magnetoresistance, improving sensitivity, and making the device easy to use.
For example, slight differences between artificial superlattice films as they grow cause slight anisotropic differences of the films even if efforts are made to grow the films under the same conditions. As a result, the produced artificial superlattice films may not exhibit a large magnetoresistance. It is therefore difficult to supply magnetoresistance films of stable characteristics.
In order to obtain a large magnetoresistance, i.e., a large rate of change of resistance, for artificial superlattice films, it is necessary for the external magnetic field to change in the range of from several 100 Oe to 10 kOe, which is larger than the external magnetic field change ranging from 5 to 10 Oe for the Permalloy films. Such a low sensitivity to the external magnetic field makes it impossible to use artificial superlattice films in magnetoresistance devices for magnetic recording, and also limits the range of uses as magnetic sensors.